1. Field of the Invention
This invention relates generally to microchannel arrangements, and more particularly, to a system for forming microchannel structures, particularly for the delivery of drugs, chemical agents, inks, and other fluids, with very high precision.
2. Description of the Related Art
There are a number of technological areas where it is desired to deliver a fluid with high spatial precision. In one area of technology, ink jet printers seek to place drops of ink on a page by propelling the ink out of small equally-spaced nozzles. Such printers generally are less expensive and quieter while printing than laser printers. However, their printing quality is generally not as good as that of laser printers, partially as a result of shortcomings in the nozzle structures currently being used. The realization of a low-cost high-resolution nozzle array is critical to the future of ink jet printers.
Presently, nozzle arrays made of glass fibers are widely used. Such nozzle heads are highly uniform and quite robust. They generally are fabricated by aligning cord fibers, assembling fiber arrays, and then bonding the glass array to supporting glass plates. In order to achieve the required precision in aligning the nozzles, notched structures made of silicon or glass are generally used as a supporting substructure. The spacing between neighboring notches and the wall thickness of the cord fibers become the main factors limiting the separation between the nozzles.
Another problem that is associated with glass nozzle heads is in the wiring that connects same to the host computer. Glass nozzles do not permit the direct integration of circuitry on-chip. Without addressing circuitry, each nozzle requires a separate wire for controlling the firing of the ink. Large numbers of wires cause a tethering problem, limiting the number of nozzles on a print head. A print head with only 10 to 60 nozzles then has to move across the paper being printed many times to print a single page. This results in slow printing speeds compared to other approaches.
In another technological area, it is well-known that complex biochemical reactions are the underlying mechanism on which the functionality of the nervous system is based. In order to understand better the behavior of biological neural networks, at the circuit level, it is important to be able to deliver drugs or other chemicals to highly localized areas of neural tissue in precise quantities while monitoring the responses in vivo. By way of example, specific caged molecules, such as calcium, can be delivered to influence cellular behavior, and NMDA (n-methyl-d-aspartate) can be delivered to modify synaptic activity. In these applications, it is important that the injecting device be very small so as not to disturb the neural system and that it be able to inject fluid volumes in the range of 10-1000 pl controllably.
The most commonly used techniques for injecting chemicals into brain tissue have been microiontophoresis and pressure-injection using single-barrel and multiple-barrel glass micropipettes. The responses of nearby neurons are then measured using separately positioned pipettes filled with electrolyte. These approaches typically suffer from relatively poor control in positioning the injecting pipette relative to the monitoring points. Additionally, the complicated procedures required for the assembly of multiple-barrel pipette structures also prevent them from being widely used. There is, therefore, a need for a neural drug-delivery probe that is able to deliver chemicals selectively at the cellular level as well as being able to record electrically from, and stimulate, neurons, in vivo. Such a probe should allow detailed studies of the neural responses to a variety of chemical stimuli, and would represent an important step toward improving scientific understanding of neural systems and treating a variety of neurophysiological disorders.
In the applications noted hereinabove, as well as others, there is a need for a microchannel nozzle arrangement wherein drive, sensor, and/or control circuitry can be combined with the nozzle. Such an integration of the nozzle or nozzles with associated integrated circuitry cannot be achieved with structures formed of quartz, or where the microchannel structure is constructed on top of a substrate, as this not only makes the overall structure larger, but also renders same incompatible with the use of the same area for forming associated circuitry and/or electrodes.
It is, therefore, an object of this invention to provide a system for forming a microchannel for the delivery of a fluid with very high precision, illustratively with a spatial selectivity on the order of 60 .mu.m or less.
It is another object of this invention to provide a system that achieves spatially selective fluid delivery and that is compatible with on-chip control systems.
It is also an object of this invention to provide a system that achieves spatially selective drug delivery and that is compatible with on-chip recording and stimulation systems.
It is a further object of this invention to provide an ink jet print head system.
It is additionally an object of this invention to provide an ink jet print head system that employs a silicon substrate having thereon on-chip drive systems.
It is yet a further object of this invention to provide a high resolution ink jet printing system.
It is also another object of this invention to provide an ink jet print head having multiple flow channels in a high nozzle density arrangement.
It is yet an additional object of this invention to provide a system in which plural microcapillary tubes are fabricated using lithographic processes.
It is still another object of this invention to provide a system in which a microcapillary tube is formed on a silicon wafer and combined with on-chip electronics.
It is a yet further object of this invention to provide a system in which a microcapillary tube is formed on a silicon wafer with dimensional control on the order of .+-.1 .mu.m and combined with on-chip structures such as heaters, microvalves, and integrated electronics.
It is also a further object of this invention to provide an ink jet printing head arrangement that can achieve printing resolution greater than 1000 dots per inch (dpi).
It is additionally another object of this invention to provide an ink jet printing head arrangement that can be fabricated, with heaters, using just five masks.
A still further object of this invention is to provide a microchannel arrangement wherein fluid flow therethrough can precisely be determined.